Prime Minister Kevin Rudd has accused Barnaby Joyce of irresponsibility after the Opposition's new finance spokesman suggested the United States may default on its debt and force the world into an economic meltdown.

The outspoken Queensland senator has also called for China to be banned from investing in Australia's resources sector and says divestiture laws should be strengthened to break up the power of the big four Australian banks.

"For someone, as the alternative finance minister of Australia, to run around the place saying America could default, Australian state governments could default, that's not responsible economic policy," he said.

"That's shooting from the lip, making it up on the run, I think being very, very irresponsible about basic Australian interests."

In his comments, Senator Joyce questioned why the Copenhagen climate talks were taking place while there were other equally important issues to consider.

And he says Australia has to prepare for the possible fallout if the US defaults on its debts.

"You'd have to look at what would happen to world trade," he said.

"What will be the effect then on the demand for Australian resources? Obviously that would go through the floor, and you know, how would Australia go forward in a position where the dynamics of the global economy are all changed?"

In reference to the banks, Senator Joyce says stronger divestiture powers would break up the four major banks.

"Australia has divestiture powers but not to the extent that the United States has them or England has them," he said.

"We've heard Mr Rudd who goes out and complains about the banks, complains bitterly, beats his chest and points fingers at the banks, but he's not prepared to put anything on the table into how he'll deal with it.

"If we had the capacity of stronger divestiture powers, at least you'd have, you know, capacity to deal with the problems that the Labor Party has brought about.

"With a loss of competition, obviously interest rates go up. There is no resolve to a centralisation of the market if you don't have a stronger form of divestiture power."

Senator Joyce says there will hopefully be enough time before the next election to detail some policy work to back up his assertions.

"But it's the issue of what is Mr Rudd's solution, he is actually the Prime Minister," he said.

"Why don't people discuss that this is a problem for the United States or the UK? Remember that their divestiture powers are way in excess of ours."

Financial Services Minister Chris Bowen says the Government is already supporting smaller banks to stay in the market.

He says Senator Joyce has populist and unworkable ideas.

"Barnaby Joyce says it's too interventionist to see the Government introducing market signals in a price on carbon," he said.

"But on the other hand he says it's okay to send a message to Australian businesses that a Liberal-National Party government may come in at any time and break up your business. Barnaby Joyce is a very worrying prospect for Australian business. He's erratic and irresponsible."

Senator Joyce is also calling for a total ban on Chinese sovereign investment in Australia.

"There has to be consideration as to what extent you want a state-owned enterprise, China or otherwise, a state-owned enterprise will be the owner of your mineral wealth, our nation of Australia's sovereign wealth in the ground," he says.

"If there is the ownership by another nation's government of your assets in the ground then quite obviously there's confusion that goes into your commercial arrangement of that.

"You are now dealing, in that instance, with another nation's government, not a corporation and if you deny that there is then confusion then you should explain that to Stern Hu currently in jail in China."